Valladolid is a colonial town on top of a Maya one, and its own attractions are modest — a convent, a long main street, the Cenote Zací in the middle of town. What makes it worth basing yourself here is what is within an hour.
Chichén Itzá is forty minutes west. Staying in Valladolid rather than on the coast means arriving at opening time, before the Cancún coaches and before the heat; by eleven the site is a different and worse experience.
Ek Balam, half an hour north, is the better ruin for some tastes: smaller, quieter, with a stucco frieze of winged figures preserved under a collapsed wall, and a main pyramid you are still allowed to climb.
The cenotes are everywhere. Dzitnup and Samulá, both a few kilometres out, are caverns with a shaft of light falling into clear water; Suytun has the famous stone platform; Oxman and Hubikú are set in old haciendas. The crowded ones are crowded by mid-morning and the countryside has dozens that are not.
Further out: Río Lagartos for the flamingos, Cobá in the jungle to the southeast, and Izamal, the yellow town, to the west.